Pressure control for hydraulic presses



1947- y. w. PETERSON ETAL 2,426,411

PRESSURE CONTROL FOR HYDRAULIC PRESSES I s sheets-sheet 1 Filed Sept. 8, 1941 v. w. PETERSON ETAL PRESSURE CONTROL FOR HYDRAULIC YRESSES Filed Sept. 8, i941 Aug. 26; 1947.

Patented Aug.-26, 1947 7 UNITED STATES PATENT OFFICE PRESSURE ooN'rRoL FOR HYDRAULIC PRESSES Victor W. Peterson and Otto 1. Mal a, Chicago, v 111., assignors to Hannifin Corporation a cor- V poration of Illinois Application September 8, 1941, Serial No. 409,984

This invention relates to presses and the like and, among other objects, aims to provide an improvedand simplified fluid operated press having sensitive pressure control.

The nature of the invention may be readily understood by reference to one illustrative press embodying the invention and shown in the accompanying drawings. I

In said drawings:

Fig. ,l is a front elevation of a press equipped for straightening shafts and the like;

Fig. 2 is a diagrammatic view illustrating the operation and control of the press;

Fig. 3 is a similar diagrammatic View; wherein the control mechanism is fully hydraulic;

Fig. 4 is a sectional view showing further details of a pressure regulating valve; and

Fig. 5 is a sectional view showing further details be capable of revealing when the pressure're-I quired to seat the bushing or other press fit part is less than that required to effect an adequately tight fit. While presses of this character have many other uses, the foregoing will be sufficient.

to illustrate their utility.

For example, if the press be employed .7 Claims. (01. 60- 52) One example of mechanism for effecting sensitive pressure control is illustrated in Fig. 2. As there shown, the pump draws liquid (preferably oil) from the reservoir through supply pipe i8 The illustrative press is shown equipped with conventional devices employed instraightening shafts or the like. The press plunger i0 is advantageously equipped with an anvil or nose block I I to apply pressure to a shaft l2 when supported by adjustably spaced anvils or bending blocks l3 resting on the press bed I4.

The press plunger in this instance is operated hydraulically with pressure supplied from a motor driven pump, such as a constant delivery rotary vane pump I5 capable of supplying fluid at pressures up to 1,000 pounds per square inch or higher.

A pump of this character is quite inexpensive,

compared with the cost of variable delivery pumps. The pump l5 and its driving motor l6 are in this instance mountedadjacent the base of the press above the fiuid reservoir I1.

and dischargesit through pipe I9 and through pressure regulatin valve 20 to a four-way valve 2| which is selectively movable to supply pressure to the head end 22 of the press cylinder ,23 through the line or to the plunger end of the cylinder through line 25. Lines carrying no substantial volume of fiuid have been illustrated in Fig. 2 by closely'spaced lines. The four-way valve in this instance is a balanced piston valve wherein the spool or piston 26 is normally urged to return positionby spring 21 and is positively moved to forward" position by actuating means here represented by a solenoid 28 whose armature when .energizedmoves valve 26 by means of plunger pin 29against the pressure of spring 21. For "forward" or downward travel of the press plunger l0, fluid enters the valve body fromsupply line and passes into line 24-the valve beingmoved to the right'in which position line 25 leading from the plunger into the cylinder discharges through the passage 3| in the valve body into discharge line 32 leading to reservoir H. For return" travel of the plunger, fluid pressure from line:-30 passes into the valve body and enters line 25 (the valve being in the position illustrated in Fig. 2). In the latter position, line 24, leading from'the head end of the cylinder,

is connectedthrough passage 3| in the valve body with discharge line 32. V Pressure controlling means, here represented by the regulating valve 20 (Fig. 4), is provided for controlling the working pressure delivered by the pump. The regulating valve in this instance comprises a pressure responsive valve 33 adapted, when the selected fluid pressure is reached, to open, allowing pressure fluid entering the port 34 to by-pass through port '35 into a return line 36 leadingv to the reservoir ll, thereby preventing the working pressure from exceeding the selected pressure. The opposite faces of valve controlling piston 31 are normally both exposed to pump 7 pressure, the lower face 38 being directly open' to pumppressure in valve chamber 39 and the opposite face 40 being exposed to pump pressure throughfa small vent opening 4| inthe piston leading to chamber 42. With balanced pressures on piston 31, the valve is held closed by a relatively light spring 43. Regulation of pressure is effected by controlling thepr'essure on the upper face 40 of the valve piston 31. When said pres-- sure is below pump pressure, piston 37 is unbalanced and opens valve 33 until the pressures on piston 31 are substantially balanced. Vent 4| is, of course, too small itself to effect equalization of pressures on opposite faces of piston 31.

In the present instance, chamber 42 is connected through passage 44 in the valve body and small vent line 45 to means represented by control valve 46 (Figs. 2 and for effecting variation in pressure in chamber 42. Valve 46 operates to vent chamber 42 at pressures determined in this instance by the operator, thereby selectively limiting the pressure delivered by the pump to the head end of the press cylinder. Valve 46 regulates the back. pressure in vent chamber 42 (and hence the pump pressure) by sensitively varying the resistance to passage of fluid through the valve. The valve embodies a variable orifice in the form of a pin 41 having a relatively long taper and being longitudinally shiftable in the port 48 for the vent line 45. The relative taper between pin 41 and orifice 46 permits a very minute and positive variation in the effective orifice in vent line 45 without risking the chattering action which frequently ensues upon close adjustment or regulation of ordinary regulating valves. The latter valves are characterized by a wide variation in effective orifice Withina very small range of movement of the valve and are prone to chatter in response to the inevitable pressure oscillation accompanying a change in valve adjustment. In the present valve, pressure oscillation cannot produce sufficient valve movement to result in closing the valve. Hence chattering is prevented and it is possible, therefore, to use the valve with assurance of smooth operation, regardless of the character of adjustment of the valve pin 41.

The illustrative valve pin has a 3 taper at its lower end 49 merging into a somewhat longer taper (1 taper) in the portion 56 of the pin immediately above the part 49. The pin'is lapped in the orifice bushing so that although being freely slidable throughout its length in the orifice bushing its upper portion will substantially completely close the orifice. Movement of the valve pin 41 in its orifice is effected in this instance by hand lever 5| fulcrumed at 52 and having an operating handle 53. The lever may also be actuated by a foot pedal 54 connected thereto through rod .55. ling lever 5| is communicated to the valve pin through the valve plunger 56 which is held in contact with the lever by the pressure of the fluid against the lower end of pin 41. Relative adjustment between pin 41 and its orifice 48 is effected in the present instance by guide pin Movement of control- 51 whose upper end is threaded-into the lower end of plunger 56. The guide pin carries a noncircular (square) portion 58 which travels in a correspondingly shaped guide passage 59 in the valve body, thereby preventing rotation of the guide pin relative to plunger 56. Rotation of the latter, therefore, serves to adjust the pin 41 relative to plunger 56 and consequently relative to its orifice. Such adjustment is employed, for example, to regulate the minimum pump pressure. The plunger 56 is held in adjusted position by means of the'packing gland 60 which carries a guide pin 6| travelling in a slot in plunger 56'. Rotation of the gland 60, therefore, serves to rotate plunger 56 for purposes of adjustment.

The minimum pressure delivered by the pump is determined by the extent to which pin 4'! throttles orifice 48 when the former is in its upper position. This pressure is regulated by adjusting the pin 4! aforesaid relative to the plunger 56. Such fluid as may seep along the face of plunger 26 may escape through port 62 into drain line 63 but most of the fluid passing through orifice 48 returns through discharge line 64 connected with line 25, the latter being connected during the advance of the press plunger, through the four-way valve to return line 32.

Solenoid 28 is controlled by an electri switch 65 in the form of a limit switch which closes upon initial movement of control lever 5|. Therefore, immediately preceding the inauguration of the forward stroke of the plunger the four-way valve is shifted to forward position. Even though the lever remains in the rapid traverse zone (that is, while the pump pressure is very low or at the minimum) nevertheless the plunger l6 and its piston 66 are caused to ad- Vance at a speed limited only by the capacity of the pump; but the plunger is able to exert little or no pressure and its movement would be arrested as soon as any resistance were encountered. Hence, if lever 5| be no further depressed, the forward advance of the press plunger would be arrested on contact with the work. Further throttling of orifice 46 (by depression of control lever 5| into the variable pressure zone) serves progressively to increase the pressure required to open regulating valve 33 and, therefore, progressively increases the pressure exerted by the press plunger. Movement of the press plunger is not required either for increase or decrease of the pressure exerted thereby since this depends solely on the extent to which orifice '48 is throttled; and variation in the orifice may be effected quite independently of movement of the press plunger. The pressure exerted by the latter is advantageously indicated in the pressure gauge 61 conveniently located in front of the operator. Maximum pressure will be developed by the pump when control lever is depressed to its lowermost position, indicated in the dot and dash line in Fig. 2.

The regulating valve (Fig. 4) is advantageously provided with an adjustable safety valve 68 adapted to connect the ventjpassage 44 to exhaust to limit the pressure delivered by the pump. Preferably this valve is set to yield at pressures slightly greater than the maximum pressure delivered on full depression of the controlling lever 5|. In the present instance, opening of the valve 68 connects vent passage 44 with a discharge passage 69 passing centrally through valve 33 and discharging into return line 36. Valve 68 is seated by spring 16 whose pressure may be adjusted by a screw threaded stem H.

To reverse the travel of the press plunger at any desired instant, it is simply necessary to return control lever 5| sufficiently to open electric switch 65 and to deenergize solenoid 28. In that event, four-way valve 2| is moved by its spring 21 to connect line 24 to d scharge and line 25 to the pump.

The return travel of the plunger may be reversed at any time simply by depressing lever 5| to permit switch 65 to close. a Means are advantageously provided for automatically arresting the return travel of the piston when it reaches a desired point. Such means are here represented by pressure unloading valve 12 (see Fig. 2) containing a spool valve 13 controlling lines 14 and 15. When moved by spring 16 to its extended position, valve '13 blocks lines 74 and 15. The

press plunger is advantageously provided with means in the form of an adjustable .cam 11 for operating va1ve'13 (to connect lines-14 and 15) when the plunger has-returned sufficiently far. So long as lines 14 and 15 remain blocked, pump pressure is delivered from line 25 through line 64 to control valve 41, thereby augmenting the pressure of spring 43 and holding the valve 33 on its seat; thereby providing maximum pump pressure for return of the press plunger. While such, maximum pump pressure is not required for all uses of the press, it may be required, for example, to withdraw the plunger when employed forpressing bushings and the like; When the plunger reaches thepredetermined limit of 'its return travel, cam 11 engages valve stem 18, operating valve 13 to unblock lines 14 and 15. Chamber 42 of the regulating valve-is thus vented through lines44, 14 and 15 to line 24 which is connected through the four-way valve to discharge. The regulating valve 33 is immediately opened to connect pump l to discharge line 36. The pump thus operates at practically zero load. A drain, line 89 connectingwith drain line 63 serves to carry away any fluid seeping past valve 13. r I

An adjustable foot valve 19 is advantageously placedin line 25 leading tc-the plunger end of thecylinder. The foot valve operates to allow fluid to flow without resistance from the pump to the plunger end of the cylinder but interposes an adjustable back pressure to flow of fluid from the plunger end of the cylinder- Any appropriate form of foot valve mayibeemployed; That here shown comprises a valve chamber 80 having a valve seat 8| against which is seated a valve cage 82 having a longitudinal passage83 closed by ball or other valve 84. The valve cage is held.

against its seat by spring 85 whose pressuremay be regulated by adjusting spring 86 to vary the pressure atwhich the valve cage may be raised from itsseat. Fluid travelling toward the plunger end of the cylinderpasses through passage'83, unseating the ball valve 84. Foot valve 19thus interposes a back pressure to the forward travel of the piston which is not quite sufiicient to balance the forward pressure on the press piston 65, thereby reducing to any desired minimum the pressure which the plunger is capable of exerting on its advance toward the work without reducing the speed of approach to the work.

By providing longitudinal adjustment of cam 11, the press plunger may be arrested at any point on its return stroke. Inthe position here shown, the camallows the plunger to return practically to the end'of the cylinder. However,

' when it is adjusted to arrest the piston at an intermediate position, a foot valve 81 is advantageously placed in line 24 to lnterpose suflicient back pressure to prevent the upward creeping of the piston under minimum pump pressure after the cam 11 has operated valve 13. Such foot valve is diagrammatically illustrated in Fig. 2. It permits free travel of fluid toward the head end of the cylinder but interposes sufficient back pressure through spring 88 to counterbalance minimum pump pressure, thereby preventing upward creeping of the plunger piston after operation of valve 13 by cam 11. I

In Fig. 3 is illustrated one form of control system which is fully hydraulic. Physicallythe sys tem is closely similar to that illustrated in Fig. 2 except (1) that the main four-way vave 2| is actuated not by a solenoid but by pressuredelivered by line 99 to the end of the spool 2B1, and (2 electric switch 65 is replaced by a four-way pilot valve 9| under the control of lever 5|. Spool 26" is in this instance provided with an additional wide land at the end to prevent escape of pressure from pilot line 90 to the discharge line 32. As here shown, the valve spool92 is biased by spring 93 which moves it to extended position upon depression of lever, 51.. In such position, port I is connected with port P from which pressure is supplied, and port 2 is connected with port T, the latter leading to the tank or reservoir l1. The valve is depressed against pressure of its spring by lever 5| when the latter approaches its upper or initial position. In such depressed position, pressure supply port P is connected with port 2 and port I is connected to discharge through. port 1 Pilot valve 9| is interposed in thepilo-t line cir-.

cuits as illustrated in Fig. 3 andas will presently be described. 1

' The operation of the system will be clear from the following: -At the beginning of a cycle when the press plunger is in its retracted position (that position being determined by the setting of the cam 11) the initial movement of operatin lever 5| allows pilot valve 9| to shift to extended position wherein ports P and 2 are connected respectively to ports I and T. Pump pressure is, applied through line 94 to line 95 (to which it is connected by communicating ports P and I) and line 90 to the piston 26 of four-way valve 2|, shifting the former to connect pump line with line 24 leading to the head end of the press cylinder. Valve 33 of the control valve is initially loaded with its spring 43 suflicientlyto develop initial crease inpressure is prevented by adequate opening of valve 33. The fluid passing through crifice 48 escapes through pilot line 96, ports 2 and T, and line 91 to discharge. Further throttling of orifice 48 by depression of lever 5| serves to increase thepressure delivered by press plunger as already described in connection with the operav tion of the system illustrated in Fig. 2. It will'be understood that after the press plunger has descended a short distance, valve 13 becomes extended and ports blocked; 7

' Upon release of control lever 5| (to causeretraction of the press plunger) pilot valve 9| is depressed to connect ports P and I respectively, with ports 2 and T. In this position, pilot line at the pilot end of four-way valve 2| is con nected (through ports I and, T) with discharge, thereby allowing valve 26 to shift (under the pressure of its spring) to connect pump line 30 with return line 25 and to connect line 24 with discharge line 32. For the return stroke of the press plunger, full pump pressure is available inasmuch as 'line45 (which vents the regulating valve) is blocked at valve 12 (to which it is connected by line 14) and control valve 41, with which its other end is connected,- being subjected to full pump pressure through the lines 94 and 96 connected through ports P and 2,'is unable, therefore, to vent the regulatingvalve despite the fact that lever 5| is in initial position.

When the plunger reaches the predetermined end of its return stroke, adjustable cam 11 shifts v,valve 13 to connect ports P and 2, thereby venting the regulating valve through lines 45, 14, 95,

2 and P of that valve .are'

port I and T to discharge. This reduces the pump pressure to its minimum and arrests the return travel of the plunger. Subsequent upward creeping is prevented by foot valve 81, as described in connection with Fig. 2.

While the apparatus has been illustrated as equipped for straightening shafts or the like, it is obvious that it may be used for many other purposes for which sensitive control of pressures is necessary or desirable. When usedas a bushing press, for example, it serves an important inspecting function by indicating (by reference'to the pressure gauge) whether the bushing fits too tightlyor not tightly enough. To facilitate the performance of this function,'the gauge 61 may be provided with limit marks by which the operator easily determines whether the pressure falls within proper tolerances.

This application is a continuation in part of our application, Serial No. 277,360, filed June 5, 1939, now abandoned.

Obviously the invention is not limited to the details of the illustrative construction since these may be variously modified. Moreover, it is not indispensable that all features be used conjointly since various features may be used to advantage in different combinations and sub-combinations.

Having described our invention, we claim:

1. A press of the character described comprising in combination a, double acting press cylinder and plunger therefor, a pump for supplying pres- 7 sure fluid to said cylinder to advance the plunger on its work stroke, a valve for alternately connecting said pump to an end of the said cylinder and connecting the other end to discharge, pressure regulating means for adjustably limiting the pump pressure and including a device under the control of theoperator whereby the force delivered by said plunger on the forward stroke may be sensitively limited and controlled by the operator during the operation of said plunger, and means for rendering said pressure regulating means ineffective on the return travel of said plunger to deliver full pump pressure to said cylinder on said return travel and for restoring the operation of said regulating means at the end of said return travel.

2. A press of the character described comprising in combination a double acting press cylinder and plunger therefor, a constant delivery pump for supplying pressure fluid to said cylinder to advance the plunger on its work stroke, a fourway valve for alternately connecting said pump to an end of the said cylinder and connecting the other end to discharge, pressure relief means associated with said pump delivery and having a valve therein operative at predetermined pressures to vent said pump to discharge to limit the pressure delivered thereby, said valve having a piston exposed on both faces to pump pressure, a vent line extending to the operators position and connected with a face of said valve piston for venting the pressure on that face, means in said line for varying the resistance to venting of said valve piston, and means for blocking said line on the return stroke of said plunger.

3. A press of the character described comprising in combination a double acting press cylinder and plunger therefor, a constant delivery pump for supplying pressure fluid to said cylinder to advance the plunger on its work stroke, a fourway valve for alternately connecting said pump to an end of the said cylinder and connecting the other end to discharge, pressure relief means associated with said pump delivery and having piston exposed on both faces to pump pressure,

a vent line extending to the operator position and connected with a face of said valve piston for venting the pressure on that face, means in said line for varying the resistanc to venting of said valve piston, and means for rendering said venting line inoperative during the return travel of said plunger but restoring it to normal function at the end of said return travel.

4. A press of the character described comprising in combination a double acting press cylinder and plunger therefor, a constant delivery pump for supplying pressure fluid to said cylinder to advance the plunger on its work stroke, a four-way valve for alternately connecting said pump to an end of the said cylinder and connecting the other end to discharge, pressure relief means associated with said pump delivery and having a valve therein operative at predetermined pressures to vent said pump to discharge to limit the pressure delivered thereby, said valve having a piston exposed on both faces to pump pressure, a vent line extending to the operators position and connected with a face of said valve piston for venting the pressure on that face, means in said line for varying the resistance tovventing of said valve piston, means for blocking said line on the return stroke of said plunger, and a valve opened by said plunger at. the end of its return travel to open said vent line and restore it to normal function.

5. A press for exciting variable force limited from substantially zero upwards, comprising in combination a double acting press cylinder and piston plunger, a pressure pump, a four-way valve for alternately connecting the head end of the cylinder to the pump and the other end to discharge and vice versa so that on the work stroke of said piston plunger full pump pressure over the entire piston area is effective in advancing the plunger, substantially unrestricted lines leading from said pump and valve to the head end of said cylinder, pressure regulating means comprising a relief valve for opening said lines to discharge for adjustably limiting th pressure delivered to said cylinder from substantially zero upwards without restricting the flow "thereto so as not to reduce the speed of advance of said plunger, means including an initially open throttling valve under the control of the operator for sensitively adjusting said relief valve to vary the pressure limit of said pump so as to limit the force exerted by said plunger on its work stroke, and means for automaticall opening said relief valve at the end of the return stroke of said plunger to open said pump to discharge and thereby reduce the load thereon.

6. A press for exerting variable force limited from substantiall zero upwards, comprising in combination a double acting press cylinder and piston plunger, a pressure pump, a four-way valve for alternately connecting the head end of the cylinder to the pump and the other end to discharge and vice versa so that on the work stroke of said piston plunger full pump pressure over the entire piston area is effective in advancing the plunger, substantially unrestricted lines leading from said pump and valve to the head end of said cylinder, pressure regulating means comprising a relief valve for opening said lines to discharge for adjustably limiting the pressure dcllvered to said cylinder from substantially zero uper, means including an initially open throttling valve under the controlzof the operator for sensitively adjusting said relief valve to vary the pressure limit of said pump so as to limit the force exerted by said plunger on its workstroke, and

- means for automatically opening said relief valve comprsing a device engaged by said plunger on its return stroke for opening said relief valve to arrest return of said plunger and reduce the load on said pump, and adjustable means for-varying the point on said return stroke at which said device is engaged so as to change the limit of said return stroke. 7

7. A press of the character described comprising in combination, a double-acting cylinder and piston for reciprocating said plunger,-a pump for delivering hydraulic pressure fluid tosaid cylinder to advance the plunger into engagement with for limiting the pressure delivered by saidpump,

control means including a vent line for operating said relief valve and a lever under the control of the operator on the work stroke of said plunger for varying the discharge orifice in said vent .Iine for sensitively varying the pressure limit at which ,said relief valve operates to permit the plunger to engage the work under controlled and limited pressure, said lever provided with means for operating said four-way valve, and mechanism block- '10 ing said vent'line on the return stroke of said plunger tomake full pump pressure available for return of said plunger.

VICTOR W. PETERSON.

OTTO J, MAHA.

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